1. Field of the Invention
The present invention refers to an improved self-locking nut, of the type having a cylindrical end compressed by a helical spring.
2. Background Information
Some types of self-locking nuts are known, having a substantially cylindrical end equipped with vertical slots, defining circular arc segments suitable to be elastically compressed by a radially operating helical external spring.
References are first made to the self-locking nut described in U.S. Pat. No. 3,417,801, in the name of Bemex, dated Dec. 24th, 1968, where a nut is claimed that has on one of its transverse faces a ring-shaped extension, equipped with radial slots delimiting some circular arc sectors compressed by an elastic ring in such a way as to perform a radial clamping action on said sectors.
Said nut has some disadvantages, substantially due to the tightness of the vertical slots provided at the cylindrical end or collar of the nut.
Said disadvantages are substantially two:
it is difficult to use the nut itself again after having unscrewed it, due to dirt and foreign materials penetrated in said slots during use, so that, in order to use the nut again, it is necessary to carry out an adequate cleaning operation with compressed air, solvents and/or mechanical means; PA1 the flexibility, and therefore compressibility, range of the walls is limited by the spring, since, after a certain bending in the radial direction, the upper edges of the circular arc segments come in mutual contact, so that the nut utility is compromised when it is applied to screws with "lean" threads. The aforementioned disadvantages have been solved by the arrangement disclosed in U.S. Pat. No. 4,893,977, in the name of Alian International A. G., dated Jan. 16th, 1990. PA1 small costs; PA1 resistance to oxidation; PA1 utilization of the nut at all temperatures. PA1 a) steel nut with low carbon content; PA1 b) steel nut with high carbon content; PA1 c) stainless steel nut.
In said Patent a self-locking nut is claimed in which, in its collar, some V or U-shaped grooves are provided, wide enough as to prevent the above-mentioned disadvantages due to the slot tightness. The disadvantages that the present Patent aims to solve are not strictly linked to this last Patent but to some current techniques, even if they are not expressly indicated.
Since the helical spring which the nut is equipped with must be protected from oxidation, a solution was to phosphatize said spring, provided in spring steel, and the other solution was to make said spring of stainless steel (when used above 250.degree. C.).
Now, it has been discovered that:
1. phosphating does not provide an adequate protection of said spring from oxidation;
2. making the spring of stainless steel generates other disadvantages, such as:
2.1. excessive costs, justified only for types of nuts provided to be used at high temperatures (above 250.degree. C.);
2.2. utilization that is advisable only for nuts provided for temperatures that are greater than 250.degree. C., since at lower temperatures it is preferable to use normal springs (made of spring steel) that have a better elasticity and consequently provides the nut with a greater braking torque;
2.3. as an average, the current springs in stainless steel give the nut a braking torque that is much lower than the one of the corresponding springs in spring steel.